The objective of this project is to develop magnetic resonance imaging (MRI) as a tool to non- invasively evaluate and monitor recovery in stroke patients. Our studies during the current funding period indicate that certain agents can enhance functional recovery after stroke in experimental animals based on histological and functional assessments. A prime candidate among restorative agents is sildenafil, a phosphodiesterase type-5 inhibitor, which has been widely used in humans to increase cyclic guanosine monophosphate (cGMP). Our data show that sildenafil significantly improves functional recovery in both young and aged animals after stroke. Hence, we will employ sildenafil in the proposed studies. We have also generated preliminary imaging data, which indicate that certain MRI methods may be sensitive to post-stroke tissue remodeling (vascular and neuronal) events that are thought to influence eventual outcome. The studies proposed in the current application expand on this theme by combining and applying these novel imaging, histological and restorative treatment strategies to assess post-stroke vascular (Aim 1) and neuronal (Aim 2) remodeling in both young and aged animals with and without restorative therapy. MRI will be used to identify, characterize and define tissue-remodeling events that contribute to improvement of late-term functional outcome after stroke. These MRI assessments will be compared and correlated to corresponding measures of tissue remodeling determined from 3D laser scanning confocal microscopy and immunohistochemistry. Finally, Aim 3 will study the relationship between the various MRI and histological indices of neuronal and vascular remodeling and will relate these data to functional outcome as measured by a battery of behavioral tests. The proposed studies are novel and innovative, moving our research away from acute diagnostics and neuroprotective therapeutic approaches for stroke treatment and toward a relatively unexplored area of late-term restorative therapy that promotes brain tissue remodeling events that ultimately improve functional outcome. If successful, these studies are expected to generate ground breaking information about post-stroke brain tissue remodeling that will be useful for monitoring stroke recovery and may lead to optimization of treatment protocols that would benefit all stroke patients.